Modulating Thermal Conductivity via Targeted Phonon Excitation.

Thermal conductivity is a critical material property in numerous applications, such as those related to thermoelectric devices and heat dissipation. Effectively modulating thermal conductivity has become a great concern in the field of heat conduction. Here, a quantum modulation strategy is proposed to modulate the thermal conductivity/heat flux by exciting targeted phonons. It shows that the thermal conductivity of graphene can be tailored in the range of 1559 W m-1 K-1 (decreased to 49%) to 4093 W m-1 K-1 (increased to 128%), compared with the intrinsic value of 3189 W m-1 K-1. The effects are also observed for graphene nanoribbons and bulk silicon. The results are obtained through both density functional theory calculations and molecular dynamics simulations. This novel modulation strategy may pave the way for quantum heat conduction.

Enhanced Far-Field Thermal Radiation through a Polaritonic Waveguide.

We experimentally demonstrate the enhancement of the far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (SiO_{2}) nanolayers supporting the propagation of surface phonon polaritons. By measuring the radiative thermal conductance between two coated Si plates, we find that its values are twice those obtained without the SiO_{2} coating. This twofold increase results from the hybridization of polaritons with guided modes inside Si and is well predicted by fluctuational electrodynamics and an analytical model based on a two-dimensional density of polariton states. These findings could be applied to thermal management in microelectronics, silicon photonics, energy conversion, atmospheric sciences, and astrophysics.

Lattice thermal conductivity and Young's modulus of XN4 (X = Be, Mg and Pt) 2D materials using machine learning interatomic potentials.

The newly synthesized BeN4 monolayer has introduced a novel group of 2D materials called nitrogen-rich 2D materials. In the present study, the anisotropic mechanical and thermal properties of three members of this group, BeN4, MgN4, and PtN4, are investigated. To this end, a machine learning-based interatomic potential (MLIP) is developed and utilized in classical molecular dynamics (MD) simulations. Mechanical properties are calculated by extracting the stress-strain curve and thermal properties by the non-equilibrium molecular dynamics (NEMD) method. The acquired results show the anisotropic Young's modulus and lattice thermal conductivity of these materials. Generally, the Young's modulus and thermal conductivity in the armchair direction are higher than in the zigzag direction. Also, the anisotropy of Young's modulus is almost constant at every temperature for BeN4 and MgN4, while for PtN4, this parameter is decreased by increasing the temperature. The findings of this research are not only evidence of the application of machine learning in MD simulations, but also provide information on the basic anisotropic mechanical and thermal properties of these newly discovered 2D nanomaterials.

Heat Conduction Theory Including Phonon Coherence.

Understanding and quantifying the fundamental physical property of coherence of thermal excitations is a long-standing and general problem in physics. The conventional theory, i.e., the phonon gas model, fails to describe coherence and its impact on thermal transport. In this Letter, we propose a general heat conduction formalism supported by theoretical arguments and direct atomic simulations, which takes into account both the conventional phonon gas model and the wave nature of thermal phonons. By naturally introducing wave packets in the heat flux from fundamental concepts, we derive an original thermal conductivity expression including coherence times and lifetimes. Our theory and simulations reveal two distinct types of coherence, i.e., intrinsic and mutual, appearing in two different temperature ranges. This contribution establishes a fundamental frame for understanding and quantifying the coherence of thermal phonons, which should have a general impact on the estimation of the thermal properties of solids.

Long-term mortality in patients with ischaemic heart failure revascularized with coronary artery bypass grafting or percutaneous coronary intervention: insights from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR).

AIMS: To compare coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI) for treatment of patients with heart failure due to ischaemic heart disease. METHODS AND RESULTS: We analysed all-cause mortality following CABG or PCI in patients with heart failure with reduced ejection fraction and multivessel disease (coronary artery stenosis >50% in ≥2 vessels or left main) who underwent coronary angiography between 2000 and 2018 in Sweden. We used a propensity score-adjusted logistic and Cox proportional-hazards regressions and instrumental variable model to adjust for known and unknown confounders. Multilevel modelling was used to adjust for the clustering of observations in a hierarchical database. In total, 2509 patients (82.9% men) were included; 35.8% had diabetes and 34.7% had a previous myocardial infarction. The mean age was 68.1 ± 9.4 years (47.8% were >70 years old), and 64.9% had three-vessel or left main disease. Primary designated therapy was PCI in 56.2% and CABG in 43.8%. Median follow-up time was 3.9 years (range 1 day to 10 years). There were 1010 deaths. Risk of death was lower after CABG than after PCI [odds ratio (OR) 0.62; 95% confidence interval (CI) 0.41-0.96; P = 0.031]. The risk of death increased linearly with quintiles of hospitals in which PCI was the preferred method for revascularization (OR 1.27, 95% CI 1.17-1.38, Ptrend < 0.001). CONCLUSION: In patients with ischaemic heart failure, long-term survival was greater after CABG than after PCI.

Outcome of PCI with Xience versus other commonly used modern drug eluting stents: A SCAAR report.

OBJECTIVES: To analyze the clinical outcome of percutaneous coronary intervention (PCI) using the Xience drug eluting stent (DES) versus other modern DES. METHODS: This retrospective study based on the Swedish Coronary Angiography and Angioplasty Registry (SCAAR) analyzed the outcome of PCI using Xience versus other commonly used modern DES, 2007 to 2017. The primary outcome measure was a combination of all-cause death, myocardial infarction (MI) and revascularisation with PCI. Angiographical outcome measures were in-stent restenosis (ISR) and stent thrombosis (ST). RESULTS: Rates of the primary outcome measure for Xience and other DES were 31.9% and 28.2% respectively, adjusted hazard ratio (HR) 0.99 (95% CI 0.95-1.03). Crude rates of ISR were 2.9% versus 2.1% over 4.3 and 2.9 years respectively, adjusted HR 0.93 (95% CI 0.81-1.06). Crude rates of ST were 0.9% versus 0.7%, adjusted HR 1.07 (95% CI 0.82-1.39). Results were consistent in all sensitivity analyses. CONCLUSIONS: This nationally complete, real-world study confirms that Xience is a safe and effective DES with low-event rates of ISR and ST. Compared with a control group containing a large proportion of thinner strut stents and absorbable polymers, Xience exhibits similar results in all important clinical endpoints.

Thermal transport in amorphous small organic materials: a mechanistic study.

Understanding the thermal transport mechanisms in amorphous organic materials is of great importance to solve hot-spot issues in organic-electronics nanodevices. Here we studied thermal transport in two popular molecular electronic materials, N,N-dicarbazolyl-3,5-benzene (mCP) and N,N'-diphenyl-N,N'-di(3-methylphenyl)-(1,1'-biphenyl)-4,4'diamine (TPD), in the amorphous state by molecular dynamics simulations. We found that due to the softness of organic materials, the low thermal conductivity of both systems can be greatly enhanced under pressure. Notably, in such systems, the convective term of heat flux provides an important contribution to thermal transport as it cross-correlates with the Virial term in the Green-Kubo formula. Mode diffusivity calculations reveal that low-frequency modes can contribute significantly to thermal transport in both mCP and TPD. By increasing the pressure, the sound velocity and relaxation time of such low-frequency modes can be enhanced, and a part of these modes converts from diffusons to propagons. The cooperation of these three effects is responsible for the strong pressure dependence of thermal transport in amorphous organic systems. Molecular pair heat flux calculations demonstrate that heat transfer mainly happens between pairs of molecules with distances below 1.4 nm. This work paves the way for the optimization of thermal transport in amorphous organic materials widely used in opto-electronics, e.g. as OLED and OPV.

Unaltered neurocardiovascular reactions to mental stress after renal sympathetic denervation.

Background: The impact of renal denervation (RDN) on muscle sympathetic nerve activity (MSNA) at rest remains controversial. Mental stress (MS) induces transient changes in sympathetic nerve activity, heart rate (HR) and blood pressure (BP). It is not known whether RDN modifies these changes.Purpose: The main objective was to assess the effect of RDN on MSNA and BP alterations during MS.Methods: In 14 patients (11 included in analysis) with resistant hypertension multi-unit MSNA, BP (Finometer ®) and HR were assessed at rest and during forced arithmetics at baseline and 6 months after RDN.Results: Systolic office BP decreased significantly 6 months after RDN (185 ± 29 vs.175 ± 33 mmHG; p = 0.04). No significant changes in MSNA at rest (68 ± 5 vs 73 ± 5 bursts/100hb; p = 0.43) were noted and no significant stress-induced change in group averaged sympathetic activity was found pre- (101 ± 24%; p = 0.9) or post-intervention (108 ± 26%; p = 0.37). Stress was associated with significant increases in mean arterial BP (p < 0.01) and HR (p < 0.01) at baseline, reactions which remained unaltered after intervention. We did not note any correlation between sympathetic nerve activity and BP changes after RDN.Conclusion: Thus, in our group of resistant hypertensives we find no support for the hypothesis that the BP-lowering effect of RDN depends on altered neurovascular responses to stress.

Pretreatment with P2Y12 receptor antagonists in ST-elevation myocardial infarction: a report from the Swedish Coronary Angiography and Angioplasty Registry.

AIMS: Pretreatment of patients with ST-elevation myocardial infarction (STEMI) with P2Y12 receptor antagonists is supported by guidelines and is a common practice despite the lack of definite evidence for its benefit. METHODS AND RESULTS: Using data from the Swedish Coronary Angiography and Angioplasty Registry on procedures between 2005 and 2016, we stratified all patients who underwent primary percutaneous coronary intervention due to STEMI in Sweden by whether or not they were pretreated with P2Y12 receptor antagonists. We investigated associations between pretreatment with P2Y12 receptor antagonists and the risk of adverse outcomes using propensity score-adjusted mixed-effects logistic regression, which accounted for clustering of patients within hospitals. The primary endpoint was all-cause death within 30 days. Secondary endpoints were infarct-related artery (IRA) occlusion, 30-day stent thrombosis, in-hospital bleeding, neurological complications, and cardiogenic shock. In total, 44 804 patients were included. They were treated with clopidogrel (N = 26 136, 58.3%), ticagrelor (N = 15 792, 35.3%), or prasugrel (N = 2352, 5.3%); 37 840 (84.5%) were pretreated, and 30 387 (67.8%) had IRA occlusion. At 30 days, there were 2488 (5.6%) deaths and 267 (0.6%) stent thrombosis. Pretreatment was not associated with better survival at 30 days [odds ratio (OR) 1.08, 95% confidence interval (CI) 0.95-1.24; P = 0.313], reduced IRA occlusion (OR 0.98, 95% CI 0.92-1.05; P = 0.608), decreased stent thrombosis (OR 0.99, 95% CI 0.69-1.43; P = 0.932), higher risk of in-hospital bleeding (OR 1.05, 95% CI 0.89-1.26; P = 0.526), or neurological complications (OR 0.72, 95% CI 0.43-1.21; P = 0.210). CONCLUSION: Pretreatment of STEMI patients with P2Y12 receptor antagonists was not associated with improved clinical outcomes.

Two-Dimensional Phonon Polariton Heat Transport.

As is well-known, the phonon and electron thermal conductivity of a thin film generally decreases as its thickness scales down to nanoscales due to size effects, which have dramatic engineering effects, such as overheating, low reliability, and reduced lifetime of processors and other electronic components. However, given that thinner films have higher surface-to-volume ratios, the predominant surface effects in these nanomaterials enable the transport of thermal energy not only inside their volumes but also along their interfaces. In polar nanofilms, this interfacial transport is driven by surface phonon polaritons, which are electromagnetic waves generated at mid-infrared frequencies mainly by the phonon-photon coupling along their surfaces. Theory predicts that these polaritons can enhance the in-plane thermal conductivity of suspended silica films to values higher than the corresponding bulk one, as their thicknesses decrease through values smaller than 200 nm. In this work, we experimentally demonstrate this thermal conductivity enhancement. The results show that the in-plane thermal conductivity of a 20 nm thick silica film at room temperature is nearly twice its lattice vibration counterpart. Additional thermal diffusivity measurements reveal that the diffusivity of a silica film also increases as its thickness decreases, such that the ratio of thermal conductivity/thermal diffusivity (volumetric heat capacity) remains nearly independent of the film thickness. The experimental results obtained here will enable one to build on recent interesting theoretical predictions, highlight the existence of a new heat channel at the nanoscale, and provide a new avenue to engineer thermally conductive nanomaterials for efficient thermal management.

Carbon-nitride 2D nanostructures: thermal conductivity and interfacial thermal conductance with the silica substrate.

The rate of heat dissipation from a 2D nanostructure strongly depends on the interfacial thermal conductance with its substrate. In this paper, the interfacial thermal conductance of carbon-nitride 2D nanostructures (C3N, C2N, C3N4's) with silica substrates was investigated using transient molecular dynamics simulations. It was found that a 2D nanostructure with higher thermal conductivity, has a lower value of interfacial thermal conductance with the silica substrate. The thermal conductivity of suspended carbon-nitride 2D nanostructures was also calculated using the Green-Kubo formalism and compared with that of graphene as a reference structure. It was found that the thermal conductivities of C3N, C2N, C3N4 (s-triazine) and C3N4 (tri-triazine) are respectively 62%, 4%, 4% and 2% that of graphene; while their interfacial thermal conductances with silica are 113%, 171%, 212% and 188% that of graphene. These different behaviors of the thermal conductivity and the interfacial thermal conductance with the substrate may be important in the thermal management of carbon-nitride 2D nanostructures in nanoelectronics.

Sustained risk of stent thrombosis and restenosis in first generation drug-eluting Stents after One Decade of Follow-up: A Report from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR).

AIMS: Long-term comparisons between Drug-eluting stent and bare metal stent are not well-studied. The aim of this study was to compare two stents that were previously frequently used in regard to long-term risk of restenosis and stent thrombosis (ST). METHODS AND RESULTS: We used data from the SCAAR registry. Consecutive procedures performed between 2004 and 2014 for stable angina, UA/NSTEMI and STEMI were included. We compared two different stents: Cordis Cypher Select (C-CS), and Boston Scientific Liberte (BS-L), modeling data with multilevel Cox proportional-hazards regression. The primary endpoint was time to first occurrence of either ST or restenosis. During the study period 2210 C-CS and 6941 B-SL were implanted in 5,314 patients. Mean follow-up time was 2,288 days for C-CS and 2,297 days for BS-L. Treatment with C-CS was associated with lower risk for restenosis or ST up to one year from index procedure (HR 0.41; 95% CI 0.32-0.52; P < .001). However, after one year of follow-up, risk was substantially higher in C-CS (HR 2.81; 95% CI 2.25-3.50; P < .001). CONCLUSION: Treatment with C-CS was not associated with better outcome than BS-L. Continuation of restenosis and ST long after the index procedure with C-CS present a major concern for patient safety.

Prognosis is similar for patients who undergo primary PCI during regular-hours and off-hours: A report from SCAAR.

BACKGROUND: Timely percutaneous coronary intervention (PCI) improves prognosis in ST-elevation myocardial infarction (STEMI). However, recent reports indicate that patients with STEMI who present during non-regular working hours (off-hours) have a worse prognosis. The aim of this study was to compare outcome between patients with STEMI who underwent primary PCI during off-hours and regular hours. METHODS: We retrieved data from the Swedish Coronary Angiography and Angioplasty Registry (SCAAR) for all patients who underwent primary PCI in Region Västra Götaland due to STEMI between January 2004 and May 2013. We modeled unadjusted and adjusted Cox proportional-hazards regression and logistic regression models for the outcomes death, cardiogenic shock, stent thrombosis and in-stent restenosis. A propensity score-adjusted Cox proportional-hazards model, which adjusted for traditional cardiovascular risk factors was predefined as the primary statistical model. Death at any time during the study period was pre-specified as primary end-point. RESULTS: During the study period 4.611 (65%) patients underwent primary PCI due to STEMI during off-hours and 2,525 (35%) during regular hours. The risk of dying was similar among the groups for the primary endpoint death at any time during the study period (HR 1.00, 95% CI 0.89-1.12, P = 0.991) and for secondary end-point death within 30 days (HR 1.03; 95% CI 0.85-1.25, P = 0.735). The risks of developing cardiogenic shock, stent thrombosis, or in-stent restenosis were similar between the groups. CONCLUSIONS: In our region, short- and long-term prognosis for patients with STEMI who undergo primary PCI is similar for patients presenting during off-hours and regular hours.

Optical Surface Tension Measurement of Two-Dimensionally Confined Liquid Surfaces.

Surface tension measurement based on spontaneous capillary wave resonance in confined micrometer-sized liquid interfaces was demonstrated. A single-beam quasi-elastic laser scattering method was used to detect the resonance. Characteristic resonant modes were observed on a 44-µm-sized circular water surface. The frequencies of the peaks agreed well with those simulated by assuming planar resonance, and the relationship was further confirmed for triangular, square, and pentagonal water surfaces. Then, the applicability of the method was successfully demonstrated by surface tension measurements of aqueous solutions of sodium dodecyl sulfate. The sensitive detection of capillary resonance opens new possibilities for the chemical and biochemical analysis of liquid interfaces.

Thermal resistance at a solid/superfluid helium interface.

Kapitza in 1941 discovered that heat flowing across a solid in contact with superfluid helium (<2 K) encounters a strong thermal resistance at the interface. Khalatnikov demonstrated theoretically that this constitutes a general phenomenon related to all interfaces at all temperatures, given the dependence of heat transmission on the acoustic impedance (sound velocity × density) of each medium. For the solid/superfluid interface, the measured transmission of heat is almost one hundred times stronger than the Khalatnikov prediction. This discrepancy could be intuitively attributed to diffuse scattering of phonons at the interface but, despite several attempts, a detailed quantitative comparison between theoretical and experimental findings to explain the occurrence of scattering and its contribution to heat transmission had been lacking. Here we show that when the thermal wavelength λ of phonons of the less dense medium (liquid (4)He) becomes comparable to the r.m.s. surface roughness σ, the heat flux crossing the interface is amplified; in particular when σ ≈ 0.33λ, a spatial resonant mechanism occurs, as proposed by Adamenko and Fuks. We used a silicon single crystal whose surface roughness was controlled and characterized. The thermal boundary resistance measurements were performed from 0.4 to 2 K at different superfluid pressures ranging from saturated vapour pressure (SVP) to above (4)He solidification, to eliminate all hypothetical artefact mechanisms. Our results demonstrate the physical conditions necessary for resonant phonon scattering to occur at all interfaces, and therefore constitute a benchmark in the design of nanoscale devices for heat monitoring.

Transformational fluctuation electrodynamics: application to thermal radiation illusion.

Thermal radiation is a universal property for all objects with temperatures above 0K. Every object with a specific shape and emissivity has its own thermal radiation signature; such signature allows the object to be detected and recognized which can be an undesirable situation. In this paper, we apply transformation optics theory to a thermal radiation problem to develop an electromagnetic illusion by controlling the thermal radiation signature of a given object. Starting from the fluctuation dissipation theorem where thermally fluctuating sources are related to the radiative losses, we demonstrate that it is possible for objects residing in two spaces, virtual and physical, to have the same thermal radiation signature if the complex permittivities and permeabilities satisfy the standard space transformations. We emphasize the invariance of the fluctuation electrodynamics physics under transformation, and show how this result allows the mimicking in thermal radiation. We illustrate the concept using the illusion paradigm in the two-dimensional space and a numerical calculation validates all predictions. Finally, we discuss limitations and extensions of the proposed technique.

Polaritonic figure of merit of plane structures.

Based on the ability of plane structures to simultaneously optimize the propagation, confinement, and energy of surface plasmon-polaritons or surface phonon-polaritons, we develop the polaritonic figure of merit Z = ßRΛ2/δ, where ßR, Λ and δ are the longitudinal wave vector, propagation length, and penetration depth, respectively. Explicit and analytical expressions of Z are derived for a single interface and a suspended thin film, as functions of the material permittivities and the film thickness. Higher Z are obtained for thinner films and smaller energy losses. The application of the obtained results for a SiC-air interface and a SiC thin film suspended in air shows that both structures are able to maximize the presence of polaritons at a frequency near to, but different than that at which the real part of the SiC permittivity exhibits a dip. Furthermore, using the temperature change of this dip, we show that the propagation length, confinement and energy of polaritons increases with its deepness, which provides an effective way to enhance the overall Z of polaritonic structures.

Hypertension is associated with increased mortality in patients with ischaemic heart disease after revascularization with percutaneous coronary intervention - a report from SCAAR.

BACKGROUND: The prognostic role of hypertension on long-term survival after percutaneous coronary intervention (PCI) is limited and inconsistent. We hypothesize that hypertension increases long-term mortality after PCI. METHODS: We analyzed data from SCAAR (Swedish Coronary Angiography and Angioplasty Registry) for all consecutive patients admitted coronary care units in Sweden between January 1995 and May 2013 and who underwent PCI due to ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI)/unstable angina (UA) or stable angina pectoris. We used Cox proportional-hazards regression for statistical modelling on complete-case data as well as on imputed data sets. We used interaction test to evaluate possible effect-modulation of hypertension on risk estimates in several pre-specified subgroups: age categories, gender, diabetes, smoking and indication for PCI (STEMI, NSTEMI/UA and stable angina). RESULTS: During the study period, 175,892 consecutive patients underwent coronary angiography due to STEMI, NSTEMI/UA or stable angina. 78,100 (44%) of these had hypertension. Median follow-up was 5.5 years. After adjustment for differences in patient's characteristics, hypertension was associated with increased risk for mortality (HR 1.12, 95% CI 1.09-1.15, p < .001). In subgroup analysis, risk was highest in patients less than 65 years, in smokers and in patients with STEMI. The risk was lowest in patients with stable angina (p < .001 for interaction test). CONCLUSION: Hypertension is associated with higher mortality in patients with STEMI, NSTEMI/UA or stable angina who are treated with PCI.

Blocking Phonon Transport by Structural Resonances in Alloy-Based Nanophononic Metamaterials Leads to Ultralow Thermal Conductivity.

Understanding the design rules to obtain materials that enable a tight control of phonon transport over a broad range of frequencies would aid major developments in thermoelectric energy harvesting, heat management in microelectronics, and information and communication technology. Using atomistic simulations we show that the metamaterials approach relying on localized resonances is very promising to engineer heat transport at the nanoscale. Combining designed resonant structures to alloying can lead to extremely low thermal conductivity in silicon nanowires. The hybridization between resonant phonons and propagating modes greatly reduces the group velocities and the phonon mean free paths in the low frequency acoustic range below 4 THz. Concurrently, alloy scattering hinders the propagation of high frequency thermal phonons. Our calculations establish a rationale between the size, shape, and period of the resonant structures, and the thermal conductivity of the nanowire, and demonstrate that this approach is even effective to block phonon transport in wavelengths much longer than the size and period of the surface resonant structures. A further consequence of using resonant structures is that they are not expected to scatter electrons, which is beneficial for thermoelectric applications.

Ultracompact interference phonon nanocapacitor for storage and lasing of coherent terahertz lattice waves.

We introduce a novel ultracompact nanocapacitor of coherent phonons formed by high-finesse interference mirrors based on atomic-scale semiconductor metamaterials. Our molecular dynamics simulations show that the nanocapacitor stores coherent monochromatic terahertz lattice waves, which can be used for phonon lasing-the emission of coherent phonons. Either one- or two-color phonon emission can be realized depending on the geometry of the nanodevice. The two-color regime of the interference phonon nanocapacitor originates from the different incidence-angle dependence of the transmission of longitudinal and transverse phonons at the respective interference antiresonances. Coherent phonon storage can be achieved by an adiabatic cooling the nanocapacitor initially thermalized at room temperature or by the pump-probe optical technique. The linewidth narrowing and the computed relative phonon participation number confirm strong phonon confinement in the ultracompact interference nanocavity by an extremely small amount of resonance defects. The emission of coherent terahertz acoustic beams from the nanocapacitor can be realized by applying a tunable reversible stress, which shifts the frequencies of the interference antiresonances.